FFinalistSouthampton · 2027
Neurology
AKT · Neurology/Infection & structural

Encephalitis

Viral brain-parenchyma infection (HSV-1 the key treatable cause)

Overview

Inflammation of the brain parenchyma, causing altered behaviour/cognition, reduced consciousness and seizures (± fever) — distinct from meningitis by the prominent cerebral dysfunction. HSV-1 (temporal-lobe) is the key treatable cause; start IV ACICLOVIR empirically and early.

Recognise

  • Altered behaviour/personality, confusion, reduced consciousness, SEIZURES, focal deficits, ± fever
  • HSV encephalitis: temporal-lobe focus → memory/behavioural change, dysphasia
  • Often a viral prodrome

Red flags

  • Reduced GCS, status epilepticus, raised ICP; delay in aciclovir worsens outcome

Differentials & how to tell them apart

Bacterial meningitismeningism dominates over cerebral dysfunction; CSF neutrophils + low glucose
Autoimmune encephalitissubacute, antibody-mediated (e.g. anti-NMDA), psychiatric features
Brain abscessring-enhancing mass, focal signs, source of infection
Status epilepticus of other causeno infective/inflammatory CSF

Investigations

LP (CSF: lymphocytes, raised protein, HSV PCR), MRI (temporal-lobe changes in HSV), EEG (lateralised periodic discharges), bloods/cultures; CT before LP if raised-ICP/focal signs.

Management

Empirical IV aciclovir immediately for suspected viral (HSV) encephalitis

  1. 1Suspected encephalitis → start IV aciclovir EMPIRICALLY and early (do not wait for the HSV PCR); LP + MRI + EEG; cover meningitis empirically if uncertain.Gate: Delaying aciclovir for confirmatory tests worsens HSV outcomes — treat first, confirm after
  2. 2Supportive care (seizures, ICP, ventilation); de-escalate when an alternative cause is confirmed; consider autoimmune encephalitis if PCR negative and picture fits.
IV aciclovir — start EMPIRICALLY and early for suspected HSV — do not wait for PCR
Anticonvulsants, supportive care — seizures, ICP

Key points

Behaviour/cognition + seizures + temporal-lobe changes = HSV encephalitis → empirical IV aciclovir NOW. The treatable cause is the reason you do not wait for the PCR.

Monitor & prognosis

GCS, seizures, CSF PCR result, MRI; response to aciclovir.

HSV encephalitis has high morbidity/mortality if treatment is delayed.

Source: NICE CKS; national encephalitis guidance